The common way to produce a dual layer single side DVD (like DVD-9) is, to bond two 0.6 mm substrates together each carrying an information layer. Another way to make a double layer disk is to use the so called 2P-process. Instead of forming one layer on each substrate, the 2P process gives rise to a single substrate structure with two internal information layers. This is not necessary for DVD-9 production, but for other multilayer formats like DVD14/18 or DVDR9.
In the first step of the 2P process a first substrate with an information layer is produced by injection moulding and coated with layer material which is appropriate for the format. Then a second substrate is produced with a second information layer—this second substrate is bonded together with the first substrate using typically an UV-curing adhesive. In the next step the 2 substrates are separated whereby the UV resin with the image of the information layer of the second substrate must remain completely at the first substrate. Depending on the application it is also possible to transfer a metallic layer in a similar way from the second to the first substrate.
For a good stamping result and an easy separation the material choice of the second substrate is important. Whereas polycarbonate is typically used for the first substrate, PMMA or other nonpolar materials are used for the second substrate.
One critical step in the process is the separation of the 2 substrates. The problem regarding the separation of the 2 substrates is that the disk shaped bonded DVD provides no suitable point for mechanical separation. Any damage on first substrate (carrying the information layer) has to be avoided. Therefore mechanical force, like mechanical gripper, can be used only with high cautiousness. A second problem to mention is that pulverized adhesive, created during the separation process can lower the quality of the media and thereby decreasing the output of the production.